Tropical Weather Discussion
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AXPZ20 KNHC 210949

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
949 UTC Mon May 21 2018

Tropical Weather Discussion for the eastern Pacific Ocean from
the Equator to 32N, east of 140W. The following information is
based on satellite imagery, weather observations, radar, and
meteorological analysis.

Based on 0600 UTC surface analysis and satellite imagery through
0900 UTC.


The monsoon trough extends from 09N84W to 10N130W, near a trough
along 133W between 10N and 15N. The intertropical convergence
zone extends west of the trough to beyond 10N140W. Scattered
moderate convection is observed from 03N to 08N between 90W and
95W. Numerous moderate to isolated strong convection is from 08N
to 10N between 108W and 112W. Scattered moderate convection is
from 10N to 12N between 132W and 136W.



A scatterometer satellite pass from 0430 UTC confirmed moderate
to fresh NW winds continue across the offshore waters of Baja
California. A concurrent altimeter satellite pass indicated 5 to
7 ft seas across these waters. Generally light to gentle variable
winds are noted over the Gulf of California, except for moderate
southerly winds across far north portions. Light NW to W winds
are noted farther south across the Mexican coastal waters. The
main forecast issue ahead will be the onset of long period SW
swell moving into the open Pacific waters off Mexico through mid
week. Large SW swell in excess of 8 ft will reach waters of
southern Mexico later today, and into the open waters off Baja
California tonight and Tue, mixing with NW swell off Baja
California Norte. Seas across the region will build to 7 to 8 ft
in this mixed swell this afternoon and spread into the mouth of
the Gulf of California early Tue.

In the Gulf of Tehuantepec, light winds will persist into Tue,
then moderate to fresh gap winds will pulse briefly as sharp
troughing shifts slowly NW across southeast Mexico.


Gulf of Papagayo: Light to gentle winds will dominate the gulf
the entire forecast period as weak pressure will prevail across
Central America. Seas of 5-8 ft are forecast over the Gulf and
nearby waters through mid week due to the strong long period SW
swell expected to arrive later this morning.

Gulf of Panama: Gentle to moderate S to SW winds are forecast
through Wed with seas of 4-6 ft in long period SW swell,
building to 5-7 ft today as the swell reaches the coasts of
Panama and Colombia.

Elsewhere, gentle to moderate SW winds are expected to the south
of the monsoon trough with light to gentle variable winds north
of trough as a weak pressure pattern remains over Central
America. Seas of 6-7 ft in building long period SW swell west of
the Galapagos Islands are expected to propagate northward
tonight through late Tue next week, building to 8 to 9 ft to the
west and northwest of the Galapagos Islands tonight through tonight.


A ridge extends from 1028 high pressure centered near 32N141W
through the Revillagigedo Islands. A scatterometer pass from 06
UTC indicated fresh strong strong trade winds 15N to 20N west of
135W, between the ridge and a weak trough along the ITCZ.
Elsewhere the ridge is maintaining generally moderate to fresh
trades north of the monsoon trough. Convergence of these winds
with light to moderate SW flow on the south side of the monsoon
trough is supporting clusters of showers and thunderstorms near
the monsoon trough west of 110W. Various recent altimeter
satellite passes indicate 4 to 6 ft seas north of 20N where winds
are lighter, and 7 to 9 ft seas in the trade wind belt between
the monsoon trough as far north as 17N as SW swell has begun to
move into the region.

The ridge will build north of 20N through into mid week,
enhancing trade winds especially near a developing weak low
pressure along the monsoon trough near 10N125W. Various recent
altimeter satellite passes continue to show SW swell in excess of
8 ft south of 10N, propagating northward. This will overtake the
region east of 130W through Tue. Looking ahead, the upper
pattern will amplify by mid week, supporting development of
another weak low along the monsoon trough west of 125W.

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